Dietary consumption of psyllium modifies the microbiota to support the development of small intestinal CD4+ CD8αα+ intraepithelial T cells 2253124

Introduction Dietary fiber has a role in changing the composition of the gut microbiota, which impacts how the immune system functions. Dietary fiber is made of complex polysaccharides with many different structures. While these fibers are mostly indigestible by the host, they are a major nutrient source for members of the microbiota that encode large enzymatic machinery to break down these complex carbohydrates. Our lab has previously shown that a low fermentable fiber diet causes impaired development of small intestinal T cell populations such as CD4+ CD8αα±, also called double positive intraepithelial lymphocytes (DP IELs), which have a local regulatory function in the small intestine; and Th17 cells, which help regulate commensal bacteria colonization. This study aims to identify fiber structures that can support the development of the DP IELs when supplemented in the diet. Methods To do this, we compared the immune cell populations in the intestines of mice fed a standard chow diet and low fiber diet to low fiber diets supplemented with specific fibers, such as inulin and psyllium. Inulin is known to improve gut health by supporting the colonization of commensal bacteria such as Bifidobacteria and Lactobacilli. Psyllium can decrease gut inflammation and improve gut health by supporting the colonization of bacteria that produce butyrate. Results Our analyses show that a diet supplemented with psyllium was able to modify the microbiota and support the development of DP IELs. Conclusion In further studies we will identify the bacteria metabolizing psyllium and the mechanism by which it restores the development of DP IELs. This knowledge will allow us to identify fibers that are beneficial for the microbiota and support our immune system.